The present invention relates to polymers that are useful in paper additives.
“Sizing,” as applied to paper, refers to a fibrous substrate's ability to resist wetting or penetration of a liquid into a paper sheet. Aqueous dispersions of alkenylsuccinic anhydride (ASA) cellulose-reactive sizing agent have been widely used in the paper and board making industry for many years, for sizing a wide variety of grades which include printing and writing grades and bleached and unbleached board grades. Cellulose-reactive alkenylsuccinic anhydride emulsions impart hydrophobic properties to the paper and board products.
Chemicals used to achieve sizing properties are known as either internal sizes or surface sizes. Internal sizes can be either rosin-based or synthetic sizes such as alkenylsuccinic anhydride, or other materials. Internal sizes are added to the paper pulp prior to sheet formation. Surface sizes are sizing agents that are added after the paper sheet has formed, most generally at the size press, although spraying applications may also be used.
A synthetic sizing agent such as alkenylsuccinic anhydride sizing agent is ordinarily applied by dispersing it in a cationic or amphoteric hydrophilic substance such as a starch or a polymer. The starch or polymer-dispersed alkenylsuccinic anhydride sizing emulsions have been added to the pulp slurry before the formation of a paper web. This type of addition of alkenylsuccinic anhydride sizing emulsions to the paper making system is commonly called wet-end addition or internal addition of alkenylsuccinic anhydride.
Papermakers would benefit from a cationic or amphoteric polymer that is different from known polymers and, preferably, that also enhances the sizing efficiency of paper products. Unfortunately, known methods and compositions have prevented papermakers from achieving this goal. Known compositions and methods require an unduly large amount of materials to size paper products. Papermakers are under pressure to improve sizing efficiency and, as such, there is an ongoing need to develop products and methods that improve sizing efficiency.
For the foregoing reasons, there is a need to develop a paper additive that improves the sizing efficiency of paper products.